1. Field of the Invention
The invention is in the field of exhaust systems for automobiles, and more specifically thin exhaust pipes for increased ground clearance on racing cars, such as stock cars, formula cars, sports cars, and the like, used on oval tracks or road course tracks.
2. Related Art
Race cars used in automobile racing are typically constructed such that only a minimal amount of clearance is maintained between the underside of the car and the surface of the roadway or track. This is done to lower the center of gravity of the car so as to improve car handling, increase resistance to rolling over, and minimize the drag due to air passing under the car. Likewise, such race cars typically have very stiff suspension systems which do not allow the car to travel as great a distance up and down nor side-to-side as a standard production car, thereby allowing less clearance between the car body and the ground. One of the problems encountered in lowering the race car closer to the race track is providing sufficient clearance between the car body and the race track for the car's exhaust system which is one of the lowest hanging components of a race car.
The problem is particularly acute on cars which race on oval race tracks, such as stock cars. The exhaust pipes of such race cars typically exit toward one or both sides of the car as compared to typical passenger cars which pipe the exhaust to the rear of the vehicle. Piping the exhaust to the side of the vehicle minimizes the length of the exhaust pipes to minimize the effects of exhaust gas back pressure which often lowers engine power output and overall engine performance. Additionally, side exhaust pipes keep the hot exhaust pipes away from the fuel cell so as to minimize the chance of a fuel fire.
Unfortunately, side exhaust pipes complicate ground clearance problems because the minimum ground clearance of the exhaust system typically occurs where the exhaust pipes cross under the longitudinally-extending main frame members of the chassis at the sides of the car. Stock cars typically race on oval tracks in a counter-clockwise rotational direction with centrifugal force causing the body and chassis of the car to lean toward the outside of the turn or toward the right side of the car. Thus, the ground clearance on the right side of the car is less during cornering and the greatest ground clearance results on the left side of the car during such cornering. However, since many cars are fueled on the left side, the exhaust pipes usually now extend to the right side of the car, the side with least clearance, to reduce the chances of fuel spilling onto the hot exhaust pipes during fueling and igniting to cause a fire.
The exhaust systems of many race cars include a pair of headers each including a plurality of primary exhaust pipes which connect at one end thereof to the cylinder block of an internal combustion engine at respective exhaust outlet ports of the engine and which converge into a single merge collector outlet at the opposite ends thereof. A secondary exhaust pipe connects the outlet of a respective merge collector to a boom tube or other type exhaust pipe, which forms a tailpipe extending from the outlet of a respective secondary exhaust pipe to the side of the car and to the atmosphere. Boom tube exhaust pipes provide a thin profile and were developed in an effort to increase the ground clearance of the exhaust system on race cars. The thin profile boom tube exhaust pipes extend from the outlets of the secondary exhaust pipes at a rearward, laterally outwardly-directed angle under the main frame members of the chassis. The outlet end of such boom tube exhaust pipes is typically manufactured in a squared-off or right angle end configuration and trimmed at installation to match exit angle and the side of the particular car on which it is installed. The secondary exhaust pipes can connect to separate tailpipes or to a single tailpipe, such as a single boom tube type tailpipe. In such instances, the inlet of the single boom tube connects to the outlets of each of the secondary exhaust pipes to combine the exhaust flow from each pipe into the single boom tube. Such exhaust systems can be made and mounted to a race car such that the entire exhaust system, including the inlets of the boom tube exhaust pipes, are at or above the lower plane of the bodies of the boom tube exhaust pipes to maximize ground clearance of the exhaust system.
In my U.S. Pat. Nos. 6,283,162 and 6,460,248, which are incorporated herein by reference, a flattened single or dual inlet boom tube exhaust pipe is disclosed for use on race cars, such as stock cars, which race on oval tracks or the like. The exhaust pipes mount to the secondary exhaust pipes of the exhaust system and to the lower frame or chassis of the car, and route exhaust gasses to one or both sides of the car while providing improved ground clearance between the exhaust pipe or pipes and the surface of the race track. The construction of the boom tube exhaust pipes comprise single or dual slightly flattened circular inlets which lead exhaust gasses into a flattened profile body constructed of formed sheet metal half shells, with the inlets at or above the lower plane of the body. One or more formed sheet metal structural ribs extend through the body and into the inlets and one or more spacer ribs support the half shells within the body. The boom tube exhaust pipes can be made with internal baffles or spiral acoustic traps so as to also be an acoustic muffler.
It is known that the performance of a race car engine can be increased in many instances by providing a connection between the secondary exhaust pipes in the exhaust system. As shown in FIGS. 17, 19, and 20 of my above-referenced U.S. Pat. Nos. 6,283,162 and 6,460,248, a crossover pipe extending between the two secondary exhaust pipes can be used to form an H-pipe assembly. A similar connection can be formed by bending the secondary exhaust pipes so that the pipes come together for a short distance in side-by-side relationship and then separate again. A hole is cut in the side of each of the two pipes where they come together and the pipes are joined, such as by welding around the mating holes, so that the interiors of the two pipes communicate through the hole. This type of connection is commonly called an X-pipe connection since the pipes generally form an X shape where they come together. A connection where multiple exhaust pipes are connected to one end of a chamber or collector and two tailpipes are connected to the opposite end of the chamber or collector is shown in Campbell U.S. Pat. No. 4,953,352. These various cross flow regions described between the secondary exhaust pipes are designed to allow fluid communication or cross flow of the exhaust gasses from each of the headers of the engine prior to entering the tailpipes. Such cross flow communication is desirable for reducing peak pressures and excessive back pressure build up of the exhaust gasses to allow more efficient exiting of exhaust gases. These arrangements can be used with one or two tailpipes as shown in FIGS. 17, 19, and 20 of my above-referenced U.S. Pat. Nos. 6,283,162 and 6,460,248.
To further improve the crossover configurations of secondary exhaust pipes when combining the exhaust flow from two secondary exhaust pipes into a single boom tube type tailpipe, I invented a Y-pipe assembly described in my U.S. Pat. No. 6,478,340, which is incorporated herein by reference. The Y-pipe assembly includes the secondary exhaust pipes and attaches to the respective ends of a pair of primary exhaust pipes or header assemblies and lead exhaust gasses from the engine of the race car to the inlet of a single boom tube exhaust pipe which mounts to the bottom portion of the frame or chassis of the race car. The Y-pipe assembly comprises a first secondary exhaust pipe comprising an inlet portion connectable to one of the header assemblies for receiving exhaust gasses therefrom and a beveled outlet portion, and a second secondary exhaust pipe comprising an inlet portion connectable to the other of the header assemblies for receiving exhaust gasses therefrom and a beveled outlet portion. The beveled outlet portions of the secondary exhaust pipes are affixed together along a respective edge of each thereof so as to merge together with respective centerlines thereof at an oblique angle to a single outlet opening which is connectable to the inlet of the boom tube. The respective secondary exhaust pipes are typically longitudinally tapered in the vertical direction with the inlet portions of the respective secondary exhaust pipes being substantially round in cross-section so as to closely fit to the respective header assembly and with the outlet portions flattened so as to be thinner at the outlet portions to form a flattened merged single outlet opening for improved ground clearance. Further, the single outlet opening of the merged outlet portion is configured to fit the inlet portion of the single boom tube exhaust pipe. The Y-pipe assembly of my U.S. Pat. No. 6,478,340 provides improved performance of race car engines and an improved exhaust system configuration for providing exhaust system clearance, but is not designed for use with two tailpipes.